/* Hashtable.java -- a class providing a basic hashtable data structure,
mapping Object --> Object
- Copyright (C) 1998, 1999, 2000 Free Software Foundation, Inc.
+ Copyright (C) 1998, 1999, 2000, 2001 Free Software Foundation, Inc.
This file is part of GNU Classpath.
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2, or (at your option)
any later version.
-
+
GNU Classpath is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// code.
/**
- * a class which implements a Hashtable data structure
+ * A class which implements a hashtable data structure.
+ * <p>
*
* This implementation of Hashtable uses a hash-bucket approach. That is:
* linear probing and rehashing is avoided; instead, each hashed value maps
* to a simple linked-list which, in the best case, only has one node.
* Assuming a large enough table, low enough load factor, and / or well
- * implemented hashCode() methods, Hashtable should provide O(1)
+ * implemented hashCode() methods, Hashtable should provide O(1)
* insertion, deletion, and searching of keys. Hashtable is O(n) in
- * the worst case for all of these (if all keys has to the same bucket).
+ * the worst case for all of these (if all keys hash to the same bucket).
+ * <p>
*
- * This is a JDK-1.2 compliant implementation of Hashtable. As such, it
+ * This is a JDK-1.2 compliant implementation of Hashtable. As such, it
* belongs, partially, to the Collections framework (in that it implements
- * Map). For backwards compatibility, it inherits from the obsolete and
+ * Map). For backwards compatibility, it inherits from the obsolete and
* utterly useless Dictionary class.
+ * <p>
*
* Being a hybrid of old and new, Hashtable has methods which provide redundant
* capability, but with subtle and even crucial differences.
* either an Iterator (which is the JDK-1.2 way of doing things) or with an
* Enumeration. The latter can end up in an undefined state if the Hashtable
* changes while the Enumeration is open.
+ * <p>
+ *
+ * Unlike HashMap, Hashtable does not accept `null' as a key value. Also,
+ * all accesses are synchronized: in a single thread environment, this is
+ * expensive, but in a multi-thread environment, this saves you the effort
+ * of extra synchronization.
+ * <p>
*
- * Unlike HashMap, Hashtable does not accept `null' as a key value.
+ * The iterators are <i>fail-fast</i>, meaning that any structural
+ * modification, except for <code>remove()</code> called on the iterator
+ * itself, cause the iterator to throw a
+ * <code>ConcurrentModificationException</code> rather than exhibit
+ * non-deterministic behavior.
*
- * @author Jon Zeppieri
- * @author Warren Levy
- * @author Bryce McKinlay
+ * @author Jon Zeppieri
+ * @author Warren Levy
+ * @author Bryce McKinlay
+ * @author Eric Blake <ebb9@email.byu.edu>
+ * @see HashMap
+ * @see TreeMap
+ * @see IdentityHashMap
+ * @see LinkedHashMap
+ * @since 1.0
*/
-public class Hashtable extends Dictionary
+public class Hashtable extends Dictionary
implements Map, Cloneable, Serializable
{
- /** Default number of buckets. This is the value the JDK 1.3 uses. Some
- * early documentation specified this value as 101. That is incorrect. */
- private static final int DEFAULT_CAPACITY = 11;
- /** The defaulty load factor; this is explicitly specified by the spec. */
+ /** Default number of buckets. This is the value the JDK 1.3 uses. Some
+ * early documentation specified this value as 101. That is incorrect.
+ */
+ private static final int DEFAULT_CAPACITY = 11;
+
+ /**
+ * The default load factor; this is explicitly specified by the spec.
+ */
private static final float DEFAULT_LOAD_FACTOR = 0.75f;
+ /**
+ * Compatible with JDK 1.0+.
+ */
private static final long serialVersionUID = 1421746759512286392L;
- /**
- * The rounded product of the capacity and the load factor; when the number
- * of elements exceeds the threshold, the Hashtable calls <pre>rehash()</pre>.
+ /**
+ * The rounded product of the capacity and the load factor; when the number
+ * of elements exceeds the threshold, the Hashtable calls
+ * <pre>rehash()</pre>.
* @serial
*/
int threshold;
- /** Load factor of this Hashtable: used in computing the threshold.
+ /**
+ * Load factor of this Hashtable: used in computing the threshold.
* @serial
*/
- float loadFactor = DEFAULT_LOAD_FACTOR;
+ final float loadFactor;
- /**
- * Array containing the actual key-value mappings
+ /**
+ * Array containing the actual key-value mappings.
*/
- transient Entry[] buckets;
+ transient HashEntry[] buckets;
- /**
- * counts the number of modifications this Hashtable has undergone, used
- * by Iterators to know when to throw ConcurrentModificationExceptions.
+ /**
+ * Counts the number of modifications this Hashtable has undergone, used
+ * by Iterators to know when to throw ConcurrentModificationExceptions.
*/
transient int modCount;
- /** the size of this Hashtable: denotes the number of key-value pairs */
+ /**
+ * The size of this Hashtable: denotes the number of key-value pairs.
+ */
transient int size;
/**
* Class to represent an entry in the hash table. Holds a single key-value
* pair. A Hashtable Entry is identical to a HashMap Entry, except that
- * `null' is not allowed for keys and values.
+ * `null' is not allowed for keys and values.
*/
- static class Entry extends BasicMapEntry
+ static class HashEntry extends BasicMapEntry
{
- Entry next;
-
- Entry(Object key, Object value)
+ /** The next entry in the linked list. */
+ HashEntry next;
+
+ /**
+ * Simple constructor.
+ * @param key the key, already guaranteed non-null
+ * @param value the value, already guaranteed non-null
+ */
+ HashEntry(Object key, Object value)
{
super(key, value);
}
+ /**
+ * Resets the value.
+ * @param newValue the new value
+ * @return the prior value
+ * @throws NullPointerException if <code>newVal</code> is null
+ */
public final Object setValue(Object newVal)
{
if (newVal == null)
}
/**
- * construct a new Hashtable with the default capacity (11) and the default
+ * Construct a new Hashtable with the default capacity (11) and the default
* load factor (0.75).
*/
public Hashtable()
}
/**
- * construct a new Hashtable from the given Map
- *
- * every element in Map t will be put into this new Hashtable
+ * Construct a new Hashtable from the given Map, with initial capacity
+ * the greater of the size of <code>m</code> or the default of 11.
+ * <p>
*
- * @param t a Map whose key / value pairs will be put into
- * the new Hashtable. <b>NOTE: key / value pairs
- * are not cloned in this constructor</b>
+ * Every element in Map m will be put into this new Hashtable.
+ *
+ * @param m a Map whose key / value pairs will be put into
+ * the new Hashtable. <b>NOTE: key / value pairs
+ * are not cloned in this constructor.</b>
+ * @throws NullPointerException if m is null, or if m contains a mapping
+ * to or from `null'.
+ * @since 1.2
*/
public Hashtable(Map m)
{
- int size = Math.max(m.size() * 2, DEFAULT_CAPACITY);
- buckets = new Entry[size];
- threshold = (int) (size * loadFactor);
+ this(Math.max(m.size() * 2, DEFAULT_CAPACITY), DEFAULT_LOAD_FACTOR);
putAll(m);
}
/**
- * construct a new Hashtable with a specific inital capacity
- *
- * @param initialCapacity the initial capacity of this Hashtable (>=0)
+ * Construct a new Hashtable with a specific inital capacity and
+ * default load factor of 0.75.
*
- * @throws IllegalArgumentException if (initialCapacity < 0)
+ * @param initialCapacity the initial capacity of this Hashtable (>=0)
+ * @throws IllegalArgumentException if (initialCapacity < 0)
*/
- public Hashtable(int initialCapacity) throws IllegalArgumentException
+ public Hashtable(int initialCapacity)
{
this(initialCapacity, DEFAULT_LOAD_FACTOR);
}
/**
- * construct a new Hashtable with a specific inital capacity and load factor
+ * Construct a new Hashtable with a specific initial capacity and
+ * load factor.
*
- * @param initialCapacity the initial capacity (>=0)
- * @param loadFactor the load factor
- *
- * @throws IllegalArgumentException if (initialCapacity < 0) ||
- * (initialLoadFactor <= 0.0)
+ * @param initialCapacity the initial capacity (>=0)
+ * @param loadFactor the load factor (>0, not NaN)
+ * @throws IllegalArgumentException if (initialCapacity < 0) ||
+ * ! (loadFactor > 0.0)
*/
public Hashtable(int initialCapacity, float loadFactor)
- throws IllegalArgumentException
{
if (initialCapacity < 0)
- throw new IllegalArgumentException("Illegal Initial Capacity: "
- + initialCapacity);
- if (loadFactor <= 0)
- throw new IllegalArgumentException("Illegal Load Factor: " + loadFactor);
-
+ throw new IllegalArgumentException("Illegal Capacity: "
+ + initialCapacity);
+ if (! (loadFactor > 0)) // check for NaN too
+ throw new IllegalArgumentException("Illegal Load: " + loadFactor);
+
if (initialCapacity == 0)
- initialCapacity = 1;
- buckets = new Entry[initialCapacity];
+ initialCapacity = 1;
+ buckets = new HashEntry[initialCapacity];
this.loadFactor = loadFactor;
- this.threshold = (int) (initialCapacity * loadFactor);
+ threshold = (int) (initialCapacity * loadFactor);
}
- /** Returns the number of key-value mappings currently in this Map */
- public int size()
+ /**
+ * Returns the number of key-value mappings currently in this hashtable.
+ * @return the size
+ */
+ public synchronized int size()
{
return size;
}
- /** returns true if there are no key-value mappings currently in this Map */
- public boolean isEmpty()
+ /**
+ * Returns true if there are no key-value mappings currently in this table.
+ * @return <code>size() == 0</code>
+ */
+ public synchronized boolean isEmpty()
{
return size == 0;
}
+ /**
+ * Return an enumeration of the keys of this table.
+ * @return the keys
+ * @see #elements()
+ * @see #keySet()
+ */
public synchronized Enumeration keys()
{
return new Enumerator(Enumerator.KEYS);
}
-
+
+ /**
+ * Return an enumeration of the values of this table.
+ * @return the values
+ * @see #keys()
+ * @see #values()
+ */
public synchronized Enumeration elements()
{
return new Enumerator(Enumerator.VALUES);
}
/**
- * returns true if this Hashtable contains a value <pre>o</pre>,
- * such that <pre>o.equals(value)</pre>.
+ * Returns true if this Hashtable contains a value <pre>o</pre>,
+ * such that <pre>o.equals(value)</pre>. This is the same as
+ * <code>containsValue()</code>, and is O(n).
+ * <p>
*
* Note: this is one of the <i>old</i> Hashtable methods which does
* not like null values; it throws NullPointerException if the
* supplied parameter is null.
*
- * @param value the value to search for in this Hashtable
- *
- * @throws NullPointerException if <pre>value</pre> is null
+ * @param value the value to search for in this Hashtable
+ * @return true if at least one key maps to the value
+ * @throws NullPointerException if <pre>value</pre> is null
+ * @see #containsValue(Object)
+ * @see #containsKey(Object)
*/
public synchronized boolean contains(Object value)
{
- for (int i = 0; i < buckets.length; i++)
+ // Check if value is null in case Hashtable is empty.
+ if (value == null)
+ throw new NullPointerException();
+
+ for (int i = buckets.length - 1; i >= 0; i--)
{
- Entry e = buckets[i];
- while (e != null)
- {
- if (value.equals(e.value))
- return true;
- e = e.next;
- }
+ HashEntry e = buckets[i];
+ while (e != null)
+ {
+ if (value.equals(e.value))
+ return true;
+ e = e.next;
+ }
}
return false;
}
/**
- * returns true if this Hashtable contains a value <pre>o</pre>, such that
- * <pre>o.equals(value)</pre>.
+ * Returns true if this Hashtable contains a value <pre>o</pre>, such that
+ * <pre>o.equals(value)</pre>. This is the new API for the old
+ * <code>contains()</code>.
*
- * @param value the value to search for in this Hashtable
- *
- * @throws NullPointerException if <pre>value</pre> is null
+ * @param value the value to search for in this Hashtable
+ * @return true if at least one key maps to the value
+ * @throws NullPointerException if <pre>value</pre> is null
+ * @see #contains(Object)
+ * @see #containsKey(Object)
+ * @since 1.2
*/
public boolean containsValue(Object value)
{
return contains(value);
}
- /**
- * returns true if the supplied object equals (<pre>equals()</pre>) a key
- * in this Hashtable
+ /**
+ * Returns true if the supplied object <pre>equals()</pre> a key
+ * in this Hashtable.
*
- * @param key the key to search for in this Hashtable
+ * @param key the key to search for in this Hashtable
+ * @return true if the key is in the table
+ * @throws NullPointerException if key is null
+ * @see #containsValue(Object)
*/
public synchronized boolean containsKey(Object key)
{
int idx = hash(key);
- Entry e = buckets[idx];
+ HashEntry e = buckets[idx];
while (e != null)
{
if (key.equals(e.key))
- return true;
- e = e.next;
+ return true;
+ e = e.next;
}
return false;
}
/**
- * return the value in this Hashtable associated with the supplied key, or <pre>null</pre>
- * if the key maps to nothing
+ * Return the value in this Hashtable associated with the supplied key,
+ * or <pre>null</pre> if the key maps to nothing.
*
- * @param key the key for which to fetch an associated value
+ * @param key the key for which to fetch an associated value
+ * @return what the key maps to, if present
+ * @throws NullPointerException if key is null
+ * @see #put(Object, Object)
+ * @see #containsKey(Object)
*/
public synchronized Object get(Object key)
{
int idx = hash(key);
- Entry e = buckets[idx];
+ HashEntry e = buckets[idx];
while (e != null)
{
if (key.equals(e.key))
- return e.value;
- e = e.next;
+ return e.value;
+ e = e.next;
}
return null;
}
/**
- * puts the supplied value into the Map, mapped by the supplied key
+ * Puts the supplied value into the Map, mapped by the supplied key.
+ * Neither parameter may be null. The value may be retrieved by any
+ * object which <code>equals()</code> this key.
*
- * @param key the key used to locate the value
- * @param value the value to be stored in the table
+ * @param key the key used to locate the value
+ * @param value the value to be stored in the table
+ * @return the prior mapping of the key, or null if there was none
+ * @throws NullPointerException if key or value is null
+ * @see #get(Object)
+ * @see Object#equals(Object)
*/
public synchronized Object put(Object key, Object value)
{
modCount++;
int idx = hash(key);
- Entry e = buckets[idx];
-
- // Hashtable does not accept null values. This method doesn't dereference
- // `value' anywhere, so check for it explicitly.
+ HashEntry e = buckets[idx];
+
+ // Check if value is null since it is not permitted.
if (value == null)
throw new NullPointerException();
while (e != null)
{
if (key.equals(e.key))
- {
- Object r = e.value;
- e.value = value;
- return r;
- }
- else
- {
- e = e.next;
- }
+ {
+ // Bypass e.setValue, since we already know value is non-null.
+ Object r = e.value;
+ e.value = value;
+ return r;
+ }
+ else
+ {
+ e = e.next;
+ }
}
-
+
// At this point, we know we need to add a new entry.
if (++size > threshold)
{
- rehash();
- // Need a new hash value to suit the bigger table.
- idx = hash(key);
+ rehash();
+ // Need a new hash value to suit the bigger table.
+ idx = hash(key);
}
- e = new Entry(key, value);
-
+ e = new HashEntry(key, value);
+
e.next = buckets[idx];
buckets[idx] = e;
-
+
return null;
}
/**
- * removes from the table and returns the value which is mapped by the
- * supplied key; if the key maps to nothing, then the table remains
- * unchanged, and <pre>null</pre> is returned
+ * Removes from the table and returns the value which is mapped by the
+ * supplied key. If the key maps to nothing, then the table remains
+ * unchanged, and <pre>null</pre> is returned.
*
- * @param key the key used to locate the value to remove
+ * @param key the key used to locate the value to remove
+ * @return whatever the key mapped to, if present
+ * @throws NullPointerException if key is null
*/
public synchronized Object remove(Object key)
{
modCount++;
int idx = hash(key);
- Entry e = buckets[idx];
- Entry last = null;
+ HashEntry e = buckets[idx];
+ HashEntry last = null;
while (e != null)
{
if (key.equals(e.key))
- {
- if (last == null)
- buckets[idx] = e.next;
- else
- last.next = e.next;
- size--;
- return e.value;
- }
- last = e;
- e = e.next;
+ {
+ if (last == null)
+ buckets[idx] = e.next;
+ else
+ last.next = e.next;
+ size--;
+ return e.value;
+ }
+ last = e;
+ e = e.next;
}
return null;
}
+ /**
+ * Copies all elements of the given map into this hashtable. However, no
+ * mapping can contain null as key or value. If this table already has
+ * a mapping for a key, the new mapping replaces the current one.
+ *
+ * @param m the map to be hashed into this
+ * @throws NullPointerException if m is null, or contains null keys or values
+ */
public synchronized void putAll(Map m)
{
- int msize = m.size();
Iterator itr = m.entrySet().iterator();
-
- for (int i=0; i < msize; i++)
+
+ for (int msize = m.size(); msize > 0; msize--)
{
Map.Entry e = (Map.Entry) itr.next();
- // Optimize in case the Entry is one of our own.
- if (e instanceof BasicMapEntry)
- {
- BasicMapEntry entry = (BasicMapEntry) e;
- put(entry.key, entry.value);
- }
- else
- {
+ // Optimize in case the Entry is one of our own.
+ if (e instanceof BasicMapEntry)
+ {
+ BasicMapEntry entry = (BasicMapEntry) e;
+ put(entry.key, entry.value);
+ }
+ else
+ {
put(e.getKey(), e.getValue());
- }
+ }
}
}
-
+
+ /**
+ * Clears the hashtable so it has no keys. This is O(1).
+ */
public synchronized void clear()
{
modCount++;
- for (int i=0; i < buckets.length; i++)
- {
- buckets[i] = null;
- }
+ Arrays.fill(buckets, null);
size = 0;
}
- /**
- * returns a shallow clone of this Hashtable (i.e. the Map itself is cloned,
- * but its contents are not)
+ /**
+ * Returns a shallow clone of this Hashtable. The Map itself is cloned,
+ * but its contents are not. This is O(n).
+ *
+ * @return the clone
*/
public synchronized Object clone()
{
}
catch (CloneNotSupportedException x)
{
+ // This is impossible.
}
- copy.buckets = new Entry[buckets.length];
-
- for (int i=0; i < buckets.length; i++)
+ copy.buckets = new HashEntry[buckets.length];
+
+ for (int i = buckets.length - 1; i >= 0; i--)
{
- Entry e = buckets[i];
- Entry last = null;
-
- while (e != null)
- {
- if (last == null)
- {
- copy.buckets[i] = new Entry(e.key, e.value);
- last = copy.buckets[i];
+ HashEntry e = buckets[i];
+ HashEntry last = null;
+
+ while (e != null)
+ {
+ if (last == null)
+ {
+ last = new HashEntry(e.key, e.value);
+ copy.buckets[i] = last;
}
- else
+ else
{
- last.next = new Entry(e.key, e.value);
- last = last.next;
- }
- e = e.next;
- }
+ last.next = new HashEntry(e.key, e.value);
+ last = last.next;
+ }
+ e = e.next;
+ }
}
return copy;
}
-
+
+ /**
+ * Converts this Hashtable to a String, surrounded by braces (<pre>'{'</pre>
+ * and <pre>'}'</pre>), key/value pairs listed with an equals sign between,
+ * (<pre>'='</pre>), and pairs separated by comma and space
+ * (<pre>", "</pre>).
+ * <p>
+ *
+ * NOTE: if the <code>toString()</code> method of any key or value
+ * throws an exception, this will fail for the same reason.
+ *
+ * @return the string representation
+ */
public synchronized String toString()
{
- Iterator entries = entrySet().iterator();
+ // Since we are already synchronized, and entrySet().iterator()
+ // would repeatedly re-lock/release the monitor, we directly use the
+ // unsynchronized HashIterator instead.
+ Iterator entries = new HashIterator(HashIterator.ENTRIES);
StringBuffer r = new StringBuffer("{");
- for (int pos = 0; pos < size; pos++)
+ for (int pos = size; pos > 0; pos--)
{
r.append(entries.next());
- if (pos < size - 1)
- r.append(", ");
+ if (pos > 1)
+ r.append(", ");
}
r.append("}");
- return r.toString();
+ return r.toString();
}
- /** returns a "set view" of this Hashtable's keys */
+ /**
+ * Returns a "set view" of this Hashtable's keys. The set is backed by
+ * the hashtable, so changes in one show up in the other. The set supports
+ * element removal, but not element addition. The set is properly
+ * synchronized on the original hashtable. The set will throw a
+ * {@link NullPointerException} if null is passed to <code>contains</code>,
+ * <code>remove</code>, or related methods.
+ *
+ * @return a set view of the keys
+ * @see #values()
+ * @see #entrySet()
+ * @since 1.2
+ */
public Set keySet()
{
- // Create a synchronized AbstractSet with custom implementations of those
- // methods that can be overriden easily and efficiently.
+ // Create a synchronized AbstractSet with custom implementations of those
+ // methods that can be overridden easily and efficiently.
Set r = new AbstractSet()
{
public int size()
{
return size;
}
-
+
public Iterator iterator()
{
return new HashIterator(HashIterator.KEYS);
}
-
+
public void clear()
{
Hashtable.this.clear();
{
return Hashtable.this.containsKey(o);
}
-
+
public boolean remove(Object o)
{
return (Hashtable.this.remove(o) != null);
}
};
- return Collections.synchronizedSet(r);
+ // We must specify the correct object to synchronize upon, hence the
+ // use of a non-public API
+ return new Collections.SynchronizedSet(this, r);
}
-
- /** Returns a "collection view" (or "bag view") of this Hashtable's values.
- */
+
+
+ /**
+ * Returns a "collection view" (or "bag view") of this Hashtable's values.
+ * The collection is backed by the hashtable, so changes in one show up
+ * in the other. The collection supports element removal, but not element
+ * addition. The collection is properly synchronized on the original
+ * hashtable. The collection will throw a {@link NullPointerException}
+ * if null is passed to <code>contains</code> or related methods, but not
+ * if passed to <code>remove</code> or related methods.
+ *
+ * @return a bag view of the values
+ * @see #keySet()
+ * @see #entrySet()
+ * @since 1.2
+ */
public Collection values()
{
// We don't bother overriding many of the optional methods, as doing so
{
return size;
}
-
+
public Iterator iterator()
{
return new HashIterator(HashIterator.VALUES);
}
-
+
public void clear()
{
Hashtable.this.clear();
}
+
+ // Override this so that we check for null
+ public boolean contains(Object o)
+ {
+ return Hashtable.this.contains(o);
+ }
};
-
- return Collections.synchronizedCollection(r);
+
+ // We must specify the correct object to synchronize upon, hence the
+ // use of a non-public API
+ return new Collections.SynchronizedCollection(this, r);
}
- /** Returns a "set view" of this Hashtable's entries. */
+ /**
+ * Returns a "set view" of this Hashtable's entries. The set is backed by
+ * the hashtable, so changes in one show up in the other. The set supports
+ * element removal, but not element addition. The set is properly
+ * synchronized on the original hashtable. The set will throw a
+ * {@link NullPointerException} if the Map.Entry passed to
+ * <code>contains</code>, <code>remove</code>, or related methods returns
+ * null for <code>getKey</code>, but not if the Map.Entry is null or
+ * returns null for <code>getValue</code>.
+ * <p>
+ *
+ * Note that the iterators for all three views, from keySet(), entrySet(),
+ * and values(), traverse the hashtable in the same sequence.
+ *
+ * @return a set view of the entries
+ * @see #keySet()
+ * @see #values()
+ * @see Map.Entry
+ * @since 1.2
+ */
public Set entrySet()
{
- // Create an AbstractSet with custom implementations of those methods that
- // can be overriden easily and efficiently.
+ // Create an AbstractSet with custom implementations of those methods that
+ // can be overridden easily and efficiently.
Set r = new AbstractSet()
{
public int size()
{
return size;
}
-
+
public Iterator iterator()
{
return new HashIterator(HashIterator.ENTRIES);
}
-
+
public void clear()
{
Hashtable.this.clear();
public boolean contains(Object o)
{
- if (!(o instanceof Map.Entry))
- return false;
- Map.Entry me = (Map.Entry) o;
- Entry e = getEntry(me);
- return (e != null);
+ return getEntry(o) != null;
}
-
+
public boolean remove(Object o)
{
- if (!(o instanceof Map.Entry))
- return false;
- Map.Entry me = (Map.Entry) o;
- Entry e = getEntry(me);
- if (e != null)
- {
- Hashtable.this.remove(e.key);
- return true;
- }
- return false;
+ HashEntry e = getEntry(o);
+ if (e != null)
+ {
+ Hashtable.this.remove(e.key);
+ return true;
+ }
+ return false;
}
};
-
- return Collections.synchronizedSet(r);
+
+ // We must specify the correct object to synchronize upon, hence the
+ // use of a non-public API
+ return new Collections.SynchronizedSet(this, r);
}
-
- /** returns true if this Hashtable equals the supplied Object <pre>o</pre>;
- * that is:
+
+ /**
+ * Returns true if this Hashtable equals the supplied Object <pre>o</pre>.
+ * As specified by Map, this is:
* <pre>
- * if (o instanceof Map)
- * and
- * o.keySet().equals(keySet())
- * and
- * for each key in o.keySet(), o.get(key).equals(get(key))
- *</pre>
+ * (o instanceof Map) && entrySet().equals(((Map) o).entrySet());
+ * </pre>
+ *
+ * @param o the object to compare to
+ * @return true if o is an equal map
+ * @since 1.2
*/
public boolean equals(Object o)
{
+ // no need to synchronize, entrySet().equals() does that
if (o == this)
return true;
if (!(o instanceof Map))
return false;
- Map m = (Map) o;
- Set s = m.entrySet();
- Iterator itr = entrySet().iterator();
-
- if (m.size() != size)
- return false;
-
- for (int pos = 0; pos < size; pos++)
- {
- if (!s.contains(itr.next()))
- return false;
- }
- return true;
+ return entrySet().equals(((Map) o).entrySet());
}
-
- /** a Map's hashCode is the sum of the hashCodes of all of its
- Map.Entry objects */
- public int hashCode()
+
+ /**
+ * Returns the hashCode for this Hashtable. As specified by Map, this is
+ * the sum of the hashCodes of all of its Map.Entry objects
+ *
+ * @return the sum of the hashcodes of the entries
+ * @since 1.2
+ */
+ public synchronized int hashCode()
{
+ // Since we are already synchronized, and entrySet().iterator()
+ // would repeatedly re-lock/release the monitor, we directly use the
+ // unsynchronized HashIterator instead.
+ Iterator itr = new HashIterator(HashIterator.ENTRIES);
int hashcode = 0;
- Iterator itr = entrySet().iterator();
- for (int pos = 0; pos < size; pos++)
- {
- hashcode += itr.next().hashCode();
- }
- return hashcode;
+ for (int pos = size; pos > 0; pos--)
+ hashcode += itr.next().hashCode();
+
+ return hashcode;
}
-
- /** Return an index in the buckets array for `key' based on its hashCode() */
+
+ /**
+ * Helper method that returns an index in the buckets array for `key'
+ * based on its hashCode().
+ *
+ * @param key the key
+ * @return the bucket number
+ * @throws NullPointerException if key is null
+ */
private int hash(Object key)
{
return Math.abs(key.hashCode() % buckets.length);
}
- private Entry getEntry(Map.Entry me)
+ /**
+ * Helper method for entrySet(), which matches both key and value
+ * simultaneously.
+ *
+ * @param o the entry to match
+ * @return the matching entry, if found, or null
+ * @throws NullPointerException if me.getKey() returns null
+ * @see #entrySet()
+ */
+ private HashEntry getEntry(Object o)
{
+ if (!(o instanceof Map.Entry))
+ return null;
+ Map.Entry me = (Map.Entry) o;
int idx = hash(me.getKey());
- Entry e = buckets[idx];
+ HashEntry e = buckets[idx];
while (e != null)
{
if (e.equals(me))
- return e;
- e = e.next;
+ return e;
+ e = e.next;
}
return null;
}
-
- /**
- * increases the size of the Hashtable and rehashes all keys to new array
- * indices; this is called when the addition of a new value would cause
- * size() > threshold. Note that the existing Entry objects are reused in
+
+ /**
+ * Increases the size of the Hashtable and rehashes all keys to new array
+ * indices; this is called when the addition of a new value would cause
+ * size() > threshold. Note that the existing Entry objects are reused in
* the new hash table.
+ * <p>
+ *
+ * This is not specified, but the new size is twice the current size plus
+ * one; this number is not always prime, unfortunately.
*/
protected void rehash()
{
- Entry[] oldBuckets = buckets;
-
+ HashEntry[] oldBuckets = buckets;
+
int newcapacity = (buckets.length * 2) + 1;
threshold = (int) (newcapacity * loadFactor);
- buckets = new Entry[newcapacity];
-
- for (int i = 0; i < oldBuckets.length; i++)
+ buckets = new HashEntry[newcapacity];
+
+ for (int i = oldBuckets.length - 1; i >= 0; i--)
{
- Entry e = oldBuckets[i];
+ HashEntry e = oldBuckets[i];
while (e != null)
- {
- int idx = hash(e.key);
- Entry dest = buckets[idx];
-
- if (dest != null)
- {
- while (dest.next != null)
- dest = dest.next;
- dest.next = e;
- }
- else
- {
- buckets[idx] = e;
- }
-
- Entry next = e.next;
- e.next = null;
- e = next;
- }
+ {
+ int idx = hash(e.key);
+ HashEntry dest = buckets[idx];
+
+ if (dest != null)
+ {
+ while (dest.next != null)
+ dest = dest.next;
+ dest.next = e;
+ }
+ else
+ {
+ buckets[idx] = e;
+ }
+
+ HashEntry next = e.next;
+ e.next = null;
+ e = next;
+ }
}
}
/**
* Serializes this object to the given stream.
- * @serialdata the <i>capacity</i>(int) that is the length of the
- * bucket array, the <i>size</i>(int) of the hash map are emitted
- * first. They are followed by size entries, each consisting of
- * a key (Object) and a value (Object).
+ *
+ * @param s the stream to write to
+ * @throws IOException if the underlying stream fails
+ * @serialData the <i>capacity</i>(int) that is the length of the
+ * bucket array, the <i>size</i>(int) of the hash map
+ * are emitted first. They are followed by size entries,
+ * each consisting of a key (Object) and a value (Object).
*/
- private void writeObject(ObjectOutputStream s) throws IOException
+ private synchronized void writeObject(ObjectOutputStream s)
+ throws IOException
{
- // the threshold and loadFactor fields
+ // Write the threshold and loadFactor fields.
s.defaultWriteObject();
s.writeInt(buckets.length);
s.writeInt(size);
- Iterator it = entrySet().iterator();
+ // Since we are already synchronized, and entrySet().iterator()
+ // would repeatedly re-lock/release the monitor, we directly use the
+ // unsynchronized HashIterator instead.
+ Iterator it = new HashIterator(HashIterator.ENTRIES);
while (it.hasNext())
{
- Map.Entry entry = (Map.Entry) it.next();
- s.writeObject(entry.getKey());
- s.writeObject(entry.getValue());
+ HashEntry entry = (HashEntry) it.next();
+ s.writeObject(entry.key);
+ s.writeObject(entry.value);
}
}
/**
* Deserializes this object from the given stream.
- * @serialdata the <i>capacity</i>(int) that is the length of the
- * bucket array, the <i>size</i>(int) of the hash map are emitted
- * first. They are followed by size entries, each consisting of
- * a key (Object) and a value (Object).
+ *
+ * @param s the stream to read from
+ * @throws ClassNotFoundException if the underlying stream fails
+ * @throws IOException if the underlying stream fails
+ * @serialData the <i>capacity</i>(int) that is the length of the
+ * bucket array, the <i>size</i>(int) of the hash map
+ * are emitted first. They are followed by size entries,
+ * each consisting of a key (Object) and a value (Object).
*/
private void readObject(ObjectInputStream s)
throws IOException, ClassNotFoundException
{
- // the threshold and loadFactor fields
+ // Read the threshold and loadFactor fields.
s.defaultReadObject();
- int capacity = s.readInt();
+ // Read and use capacity.
+ buckets = new HashEntry[s.readInt()];
int len = s.readInt();
- size = 0;
- modCount = 0;
- buckets = new Entry[capacity];
- for (int i = 0; i < len; i++)
- {
- Object key = s.readObject();
- Object value = s.readObject();
- put(key, value);
- }
+ // Read and use key/value pairs.
+ for ( ; len > 0; len--)
+ put(s.readObject(), s.readObject());
}
/**
- * a class which implements the Iterator interface and is used for
- * iterating over Hashtables;
- * this implementation is parameterized to give a sequential view of
- * keys, values, or entries; it also allows the removal of elements,
- * as per the Javasoft spec.
+ * A class which implements the Iterator interface and is used for
+ * iterating over Hashtables.
+ * This implementation is parameterized to give a sequential view of
+ * keys, values, or entries; it also allows the removal of elements,
+ * as per the Javasoft spec. Note that it is not synchronized; this is
+ * a performance enhancer since it is never exposed externally and is
+ * only used within synchronized blocks above.
*
- * @author Jon Zeppieri
+ * @author Jon Zeppieri
*/
class HashIterator implements Iterator
{
+ /** "enum" of iterator types. */
static final int KEYS = 0,
VALUES = 1,
- ENTRIES = 2;
-
- // The type of this Iterator: KEYS, VALUES, or ENTRIES.
- int type;
- // The number of modifications to the backing Hashtable that we know about.
- int knownMod;
- // The total number of elements returned by next(). Used to determine if
- // there are more elements remaining.
- int count;
- // Current index in the physical hash table.
- int idx;
- // The last Entry returned by a next() call.
- Entry last;
- // The next entry that should be returned by next(). It is set to something
- // if we're iterating through a bucket that contains multiple linked
- // entries. It is null if next() needs to find a new bucket.
- Entry next;
-
- /* Construct a new HashIterator with the supplied type:
- KEYS, VALUES, or ENTRIES */
+ ENTRIES = 2;
+
+ /**
+ * The type of this Iterator: {@link #KEYS}, {@link #VALUES},
+ * or {@link #ENTRIES}.
+ */
+ final int type;
+ /**
+ * The number of modifications to the backing Hashtable that we know about.
+ */
+ int knownMod = modCount;
+ /** The number of elements remaining to be returned by next(). */
+ int count = size;
+ /** Current index in the physical hash table. */
+ int idx = buckets.length;
+ /** The last Entry returned by a next() call. */
+ HashEntry last;
+ /**
+ * The next entry that should be returned by next(). It is set to something
+ * if we're iterating through a bucket that contains multiple linked
+ * entries. It is null if next() needs to find a new bucket.
+ */
+ HashEntry next;
+
+ /**
+ * Construct a new HashIterator with the supplied type.
+ * @param type {@link #KEYS}, {@link #VALUES}, or {@link #ENTRIES}
+ */
HashIterator(int type)
{
this.type = type;
- knownMod = Hashtable.this.modCount;
- count = 0;
- idx = buckets.length;
}
- /** returns true if the Iterator has more elements */
+ /**
+ * Returns true if the Iterator has more elements.
+ * @return true if there are more elements
+ * @throws ConcurrentModificationException if the hashtable was modified
+ */
public boolean hasNext()
{
- if (knownMod != Hashtable.this.modCount)
- throw new ConcurrentModificationException();
- return count < size;
+ if (knownMod != modCount)
+ throw new ConcurrentModificationException();
+ return count > 0;
}
- /** Returns the next element in the Iterator's sequential view. */
+ /**
+ * Returns the next element in the Iterator's sequential view.
+ * @return the next element
+ * @throws ConcurrentModificationException if the hashtable was modified
+ * @throws NoSuchElementException if there is none
+ */
public Object next()
{
- if (knownMod != Hashtable.this.modCount)
- throw new ConcurrentModificationException();
- if (count == size)
+ if (knownMod != modCount)
+ throw new ConcurrentModificationException();
+ if (count == 0)
throw new NoSuchElementException();
- count++;
- Entry e = null;
- if (next != null)
- e = next;
+ count--;
+ HashEntry e = next;
while (e == null)
- {
- e = buckets[--idx];
- }
+ e = buckets[--idx];
next = e.next;
last = e;
return e;
}
- /**
- * Removes from the backing Hashtable the last element which was fetched
+ /**
+ * Removes from the backing Hashtable the last element which was fetched
* with the <pre>next()</pre> method.
+ * @throws ConcurrentModificationException if the hashtable was modified
+ * @throws IllegalStateException if called when there is no last element
*/
public void remove()
{
- if (knownMod != Hashtable.this.modCount)
- throw new ConcurrentModificationException();
+ if (knownMod != modCount)
+ throw new ConcurrentModificationException();
if (last == null)
- {
- throw new IllegalStateException();
- }
- else
- {
- Hashtable.this.remove(last.key);
- knownMod++;
- count--;
- last = null;
- }
+ throw new IllegalStateException();
+
+ Hashtable.this.remove(last.key);
+ knownMod++;
+ last = null;
}
}
/**
- * Enumeration view of this Hashtable, providing sequential access to its
- * elements; this implementation is parameterized to provide access either
+ * Enumeration view of this Hashtable, providing sequential access to its
+ * elements; this implementation is parameterized to provide access either
* to the keys or to the values in the Hashtable.
*
* <b>NOTE</b>: Enumeration is not safe if new elements are put in the table
* the "Java Class Libraries" book infers that modifications to the
* hashtable during enumeration causes indeterminate results. Don't do it!
*
- * @author Jon Zeppieri
+ * @author Jon Zeppieri
*/
class Enumerator implements Enumeration
{
- static final int KEYS = 0;
- static final int VALUES = 1;
-
+ /** "enum" of iterator types. */
+ static final int KEYS = 0,
+ VALUES = 1;
+
+ /**
+ * The type of this Iterator: {@link #KEYS} or {@link #VALUES}.
+ */
int type;
- // current index in the physical hash table.
+ /** Current index in the physical hash table. */
int idx;
- // the last Entry returned by nextEntry().
- Entry last;
- // Entry which will be returned by the next nextElement() call.
- Entry next;
-
+ /** The last Entry returned by nextEntry(). */
+ HashEntry last;
+ /** Entry which will be returned by the next nextElement() call. */
+ HashEntry next;
+
+ /**
+ * Construct the enumeration.
+ * @param type either {@link #KEYS} or {@link #VALUES}.
+ */
Enumerator(int type)
{
this.type = type;
this.idx = buckets.length;
}
-
- private Entry nextEntry()
+
+ /**
+ * Helper method to find the next entry.
+ * @return the next entry, or null
+ */
+ private HashEntry nextEntry()
{
- Entry e = null;
+ HashEntry e = null;
if (last != null)
e = last.next;
while (e == null && idx > 0)
- {
- e = buckets[--idx];
- }
+ e = buckets[--idx];
+
last = e;
return e;
}
+ /**
+ * Checks whether more elements remain in the enumeration.
+ * @return true if nextElement() will not fail.
+ */
public boolean hasMoreElements()
{
if (next != null)
return true;
next = nextEntry();
- return (next != null);
+ return next != null;
}
+ /**
+ * Returns the next element.
+ * @return the next element
+ * @throws NoSuchElementException if there is none.
+ */
public Object nextElement()
{
- Entry e = null;
+ HashEntry e;
if (next != null)
{
e = next;
- next = null;
- }
+ next = null;
+ }
else
e = nextEntry();
if (e == null)
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